With advances in autonomy, reliance on navigational devices for vehicles (ground, airborne, or space-borne) is imperative. The Global Positioning System (GPS) is the ubiquitous choice for many applications, however, GPS has several shortcomings such as radio frequency (RF) interference, jamming, signal blockage, or GPS satellite outages.
GPS utilizes a constellation of satellites, emitting radio signals, to allow a receiver to ascertain position. Instrument Landing System (ILS) uses overlapping radio signals from a ground station to allow measurement of aircraft position relative to a single, predefined approach path. The Unmanned Common Automatic Recovery System (UCARS) and Tactical Approach Landing System (TALS) utilize ground-based radar with an airborne transceiver; to determine range and position relative to an approach path; the measurements are then conveyed to the aircraft over a radio link. The Optical Landing System (OLS) utilizes visible non-coherent lights arranged such that an approaching pilot sees different patterns depending on whether the aircraft is high, low, or off-center relative to the desired approach path. Below, Table 1.1 details the shortcomings of these systems.
TABLE 1.1ShortcomingGPSILSUCARSOLSTALSHigh Radar ObservabilityxxxRF Sensing or Communication LinkxxxxRequiredDoes Not Allow for MotionxxxCompensationHigh Airborne ComplexityxxUnable to Deny Access to UnauthorizedxxxUsersUnable to Reconfigurable on the flyxxxNo Three Dimensional PositionxxMeasurementxPrecludes Use by Multiple SimultaneousxxReceiversHighly Susceptible to JammingxxxxDoes Not Provide Absolute PositionalxxxxMeasurements
Numerous attempts by others have been made to address these deficiencies, some using laser based systems. For example, U.S. Pat. No. 7,898,435 utilizes a transmitter on a vehicle, transmitting in three different directions. Reflected energy is analyzed, including Doppler shifts, to calculate altitude, ground speed, and relative wind. However, this system is not designed to measure position relative to a desired approach path, does not provide a communication method between the ground and the aircraft, and requires extensive aircraft equipment (multiple lasers in addition to sensors).
U.S. Pat. No. 4,925,303 utilizes two scanning beams originating from two different positions on an aircraft. A sensor, also on the aircraft, receives reflections from a known pattern of reflective targets on the ground to determine position, speed, and distance from the runway. However, this system relies on existing technology (ILS or MLS) to gain proximity to the runway, requires extensive ground setup, is not reconfigurable on the fly for different approach requirements, requires extensive aircraft equipment (multiple lasers in addition to sensor(s)), requires both an airborne transmitter and receiver, requires bi-directional light propagation, and does not provide a secure communication link between the ground and the aircraft.
U.S. Pat. No. 5,043,726 utilizes ground-based lasers, spatially separated. An angular and spectral sensor on the aircraft senses the incoming angles of the multiple lasers and thereby determines aircraft position relative to the lasers using triangulation. However, this system suffers from loss of precision at reasonable ranges, requires more extensive ground equipment (multiple lasers with significant spatial separation), uses a different method for beam sensing, is not easily reconfigurable, and does not provide a secure communication link between the ground and the aircraft.
U.S. Pat. No. 5,287,104 utilizes visible lasers of three defined colors, projected in a known pattern, to allow a pilot to determine position relative to approach path; this is essentially a laser-based version of the OLS system used on aircraft carriers. However, this system is specifically designed for human eye sensing, not machine sensing; relies on multiple beams of different wavelength; and does not provide any range-to-go information.
In view of the shortcomings listed above, alternative system(s) and method(s) for precision navigation are needed, specifically ones that do not rely on the RF spectrum. Details of such system(s) and method(s) are elucidated in the following description.